Development Of Fluorescent Conjugated Polymer-Based Chemosensors And Portable Corn Component Analyzer

Part A Preparation and application of fluorescent conjugated polymersConjugated polymers (CPs), a kind of very important organic semi-conductive luminescent materials, have gained extensive studies since 1977, with the discovery that polyacetylene's conductivity could be greatly enhanced by doping. Especially in the last two decades, conjugated polymers have received broad applications in the area of photoelectric devices such as CP-based LED, plastic lasers and field-effect transistor, etc, because of their superior properties in luminescence, electronics and magnetics. However, the research on using fluorescent conjugated polymers (FCPs) as sensing materials just began in the mid of 1990s. Due to the unique molecular-wire effect of FCPs, the fluorescence responses could be greatly amplified without changing the association constants with specific analytes, which provides good opportunities to design high sensitive chemo-sensors. Therefore, in recent years, FCP-based bio- and chemo- sensors have attracted increasing attentions in the detection of organic molecules, metal ions and bio-molecules, and gradually became one of the hot topics.For the applications in sensing, FCPs with ionic side-groups (also known as conjugated polyelectrolytes) have great superiorities when compared to traditional conjugated polymers that could solve in organic solvents: On one hand, the water-solubility makes them more suitable in bio-systems; And on the other hand, the existence of cations or anions provides an effective means of interaction with analytes in designing sensors; Also the sensitivity to quenchers with opposite charges is further increased to a large extent. In our work, the PPE-type conjugated polyelectrolytes have been studied in details with focuses on preparation and their applications in sensing. The main contents include:The progress, category and electronic structures of conjugated polymers are introduced in the first chapter. Also, the mechanism of signal amplification and the application of FCPs in sensing are reviewed in detail as well.In Chapter two, a novel facile synthetic route for the preparation of PPESO3 was developed. Starting from hydroquinone, only three steps were required: Under basic conditions, sulfonated receptors were installed via 1,3-propanesultone, followed by the electrophilic substitution of iodine in a mixture of glacial acetic acid and water, and PPESO3 was obtained by palladium-catalyzed cross-coupled reaction with 1,4-diethynylbenzene. Compared with the scheme reported by Tan et al., this new route is much simpler and more effective. Not only the procedure is simplified, but most importantly, the preparing difficulty, complexity and danger were greatly reduced by avoiding the use of BBr3, which will be certainly beneficial to the preparation and application of PPESO3 and other PPEs with similar structures.Chapter three to Chapter five emphasized on the application studies of PPESO3. In Chapter three, the optical property and aggregation in water of PPESO3 were discussed. Further, interactions of PPESO3 with metal ions and surfactants were investigated as well. And the results indicated that most metal ions would not interfere with PPESO₃ applied in sensing when their concentration is below 10μM. Moreover, the polymer's fluorescence could be effectively quenched by Fe³⁺, while Fe²⁺ had almost no effect. This phenomenon provides feasibility to design high sensitive sensors based on the redox of Fe²⁺/Fe³⁺. Therefore, in Chapter four, by making use of the oxidation of Fe²⁺, sensors for formaldehyde and peroxide based on the superquenching of PPESO₃ have been developed. These sensors featuring less reagents, simple structure and high sensitivity, are valuable for the detection of formaldehyde in room environment and urine glucose, respectively. In the last chapter, a general method for the detection of protease activity is discussed. BSA could greatly enhance the fluorescence of PPESO3 due to its surfactant effects, and concomitant with a significant blue-shift. However, once BSA is hydrolyzed by protease the system fluorescence would restore. By this means, one can easily monitor the activity of protease, which will certainly facilitate the discovery of drugs based on enzyme inhibitor.Part B Study on the development of fast portable NIR corn component analyzerNear infrared spectroscopy (NIRS) is an analytical technique that has progressed very rapidly in recent years. Due to its many merits, such as rapid, real-time or even on-line detection, NIRS has been widely used in agriculture, food, petroleum and pharmacy. Especially in the process of foodstuff purchasing, storage or measurement, the advantages such as fast speed and no sample pretreatment of NIRS have made it a more and more important analytical tool. As the substantial foundation, NIR instruments have also gained great developments, in which the miniature specific NIR analyzer based on filters design has obvious priorities in the detection of corn components on site.In our research, a fast portable NIR corn component analyzer based on filters has been developed. The development process and instrumental performance of the newly developed analyzer will be described in this part. First, in Chapter one, the NIR Spectroscopy was reviewed in detail, including its development, characteristics, instruments, commonly used chemometrics methods and main application fields.In Chapter two, some kinds of the algorithms for variable selection were discussed, and the method Uninformative Variables Elimination (UVE), was chosen to pick out wavelengths from corn NIR spectrum. These results provided good supports for the designing of filter based fast portable NIR corn component analyzer.Chapter three was the core content of Part B, in which the research project of this NIR corn component analyzer was fully presented: The LED array composed of ultra-bright NIR LEDs and narrow-band interference filters, together with a silicon photo-diode detector constituted the optical system. In order to improve the signal intensity and repeatability, unique optical design, silicon photo-diode with large active area and series-wound LED technique were adopted. In the controlling circuit system, the motivation of LED, photo-electric conversion, grounding and time sequence design were optimized, which greatly improved the instrumental performance. For dada processing, PLS algorithm, temperature compensation technique and multiple scatter calibration were combined to construct a robust model. And in the end of this chapter, the performance of the newly developed analyzer, including accuracy, repeatability and stability toward temperature changes, were examined systematically. And the results were satisfactory.